Automatic telephone system



Aug. 15, 1933. A TT- 1,922,237

AUTOMATI C TELEPHONE SYSTEM ori ihal Filed July 13, 1931 2 Sheets-Sheet1 IH'U'ETIEF Hlexandat Jul-m EEEEH Aug. 15, 1933. A, J, ESCOTT AUTOMATICTELEPHONE SYSTEM Original Filed July 13, 1931 2 Sheets-Sheet 2 IHUEIL DrHlexande'r Jul-m BEE 5:11

Patented Aug.15. 1933 7 I 1,922,237

UNITED STATES PATENT OFFICE Alexander John Escott, London, England,assigner to Siemens B1'otl1ers & Company Limited, London, EnglandApplication July [13. 1931', Serial Nb. 550,323, 7 e and in GreatBritain August 7, 1930.. Renewed October 17, 1932 i 20 Claims. (cine-1aThe present invention relates to automatic This may be done asfollowsjBoth Switches step telephone systems, and'more particularly tothe on receipt of the first impulse of the switch setselecting switchesfor use in such systems. ting train, one being stepped to the commence-The selecting switches employed in automatic ment of the first group ofoutlets, the other to telephone systems are usually arranged to stepthe'commencement of the second group of out- 60 in response to a trainof impulses consisting of ts. The succeeding impulses drive the switchesfrom one to ten impulses, to an initial position alternately, thatresting at the commencement at one end of a. group, of outlets, and thento of the first group being the first to drive, the

hunt automatically fora freeoutlet in the group. switch last drivenpreparing a circuit for the Where the selecting switch is of thetypewhich driving of the other switch. At the end of the 65 has motion inone plane only, usually a rotary switch setting impulse train the switchwhich motion, and in which all the wipers on the rests at thecommencement of the earlier group switch shaft partake in the huntingmotion, it of contacts hunts over that group for a free out is sometimesarranged that the impulses take let. V

l5 ei fect on a marking switch which marks in the In order to reduce thehunting time and yet 70 banks of the selecting switch the group of outtohave-a large number of. outlets we may conlets to be searched, theselecting switch being nect the outlets of a group to a few consecutivestepped automatically to the commencement of contacts only and providethe switches with'more the marked group for a free outlet. The markthanone set of wipers andfcontact banks and ing; switch is thus usedtemporarily until a selectarrange for simultaneous. search over. all the7 ing switch has found a freeoutlet and may then wiper sets of a switch.

be released, and arrangementshave been pro- Reference will now behadtothe accompanyvided whereby a marking switch may be availing drawings.Fig. I ShOWSB/ PaiIflOf swit'ches able in common to a number ofselecting switches. embodying the inventionand suitable for use in Inthe present invention two. single-motion a register controller system.Fig. 2 shows answitches are combined toiorm a singleselector, otherembodiment whichmay beused in a direct outlets being provided in thebanks of each impulsing system.

switch, and one switch may. be used as a mark- The arrangements shown inFig. .1 will first ing switch for the other. i be considered;

30 It may be arranged that outlets of a group are The selector comprisestwo 'slng le-niotion provided in both switchesand a set of outletsswitches each having seven wipersfian'd correof a group in one switch ismarked by the other spending contact banks of 51 contacts each. switchin response to. an impulse train. and if The switch wipers aredesignated Xl-Q-X'lfor one these outlets are all busy the switch whichapswitch which will be referred to as switch xjand plied the firstmarking has. a marking applied Yl Y'l for theother switchwhichwill be re90 to it and it thereupon steps to the marked posiferred' to as switchY. Outlets to a further tion and commences hunting for a free outletswitching stage orother circuits are divided into in a further set ofoutlets in the same group. 7 groups/some oi the outlets of agroup beingcon- This arrangement, whilst suitable for use with nected to switch Xand others to switch Y. In

4.0 a system in which the selectors are set under the example taken itis assumed that there are .95

the control of a register controller in which the ten groups of eightoutlets each','the first four pause between successive impulse trainscan be outlets of a group being connected to switch Y controlled so asto permitof the complete searchand the last four outlets of the groupbeing coning of a group, may not be convenient in a direct nected toswitch X" Further, for the purpose impulsing system except for smallgroups of of equalizing the searching time for all the 190 outlets suchas lines to a small private branch groups. the groups are connected toswitch X in exchange, owing to the time requiredto step the the reverseorder to their connection to switch Y. switches to the'marked positionsand to hunt Theselector is of the type which tests free by over acomplete group of outlets. reason of battery potential on the test wire,.the In a modification suitable foruse with a direct free condition ofan outlet also being battery .l05

impulsing system, it maybe arranged that the .potential on the testwire. The impulse relay two switches comprising a selector act in turnas is designated A, the release relay B, and the dialmarkers' at eachimpulse of a train, oneswitch ling relay C. HX is the test relay forswitch X being marked by an odd number of impulses and and JHY forswitch Y. R. is a relay which conthe other switch by an even numberofimpulses. nects up test relay HY when the wipers of switch .111

Y have reached a group marked by impulses in which search is to be madeand relay P is operated when switch Y has failed to find a free outletto mark the remainder of the group to be searched for by switch X. Thedriving magnet of switch X is designated XDM and that of switch Y, YDM.

When not in use the selector rests in a normal position with its wiperson the first contacts in their banks as shown in the drawings. Forconvenience in drawing only parts of the banks have been shown, theremainder of the banks being connected in a manner similar to the partsshown.

The selector tests free by reason of a battery connection over winding(I) of relay C, wipers Y5 and X5 to wire c and when seized from aprevious switching stage relay C operates and at contact 02 opens apoint in the circuit of magnet YDM to prevent switch Y being stepped bya false impulse. Contact 04 disconnects battery from wire (1. Relay A isnow operated over wire I) from the register controller and at contact a2connects relay B to the test wire 0, and at contact a1 opens a point inthe impulsing circuit for magnet XDM. Relay B operates and locks to thetest wire over its contact b1. Contact b2 pre pares a circuit for magnetYDM, contact 123 prepares a circuit for magnet XDM and contact b4.prepares a circuit for marking switch Y, this circuit being open at thistime at contact 03.

Relay A responds to impulses and repeats them over contacts a1 and 01,low resistance winding (II) of relay C, and contact 123 to magnet XDM.Magnet XDM steps switch X in accordance with the impulses receivedand'on leaving its normal position wiper X5 opens the circuit of winding(I) of relay C. At the end of the impulse train relay C releases andconnects earth over contacts b4 and c3, and wiper X2 and the contact towhich it has been stepped to mark a group of contacts in the bank ofwiper Yd. The groups of contacts correspond to the outlets from switchY, and, as regards the first group, they are connected to contacts 2'5.The second group is connected to contacts 7l0, each succeeding groupbeing connected to four contacts, the first contacts of each group beingfive contacts apart. Contact 02 closing, acircuit is closed for magnetYDM and this magnet steps switch Y in search of the marked group, themagnet interrupting its own circuit at contact ydm. When .the

marked group isreached relay R operates over wiper Y4, the group markingcontacts in its bank and the bank of wiper X2, contacts 03, D4 to earth.Contactrl connects test relay HY to test wiper Y3 and contact 1-2prepares a holding circuit for relay R should no free outlet be foundand switch Y is stepped, to contacts 6, ll, 16succeeding groups "ofoutlets. Switch Y continues to step over the contacts of the markedgroup in search of a free outlet connected to its wipers Y6, Y7, Y3. Ifa free outlet is found relay HY operates over wiper Y3 to battery on thetest bank contact and opens the magnet circuit at contact hy i, stopping.further driving. Contact hyl short circuits the high resistance windingof relay HY to mark the outlet engaged and contacts hyZ and 71.113connect the speaking wires a and 1) through over Wipers Y6 and Y'I.Relay A releases and battery is connected from wire a at contact hy2.

Should all the outlets of the group connected to switch Y be engaged theswitch is stepped on to one of the contacts 6, 11which in the bank ofwiper Y3 are commoned and connected to relay P. Relay P operates inseries with relay HY.

The operation of relay HY opens the direct connection of battery overcontact 04 to the a wire and of relay A to the 1) wire but alternativecircuits are closed over one of the contacts 6, ll, 16in the banks of Y6and Y7 for these battery connections. The battery connection to wire atransmits a signal to the register controller which holds up furtherimpulse transmission until the battery connection is removed.

When relay P operates contact p2 connects earth over wiper Y2, one ofthe bank contacts 6, l1,--to a set of group marking contacts in the bankof wiper X4. Contact pl closes a circuit from earth overself-interrupting contact :cdm of magnet XDM, contacts had and 123 formagnet XDM. Switch X is thereupon stepped until the marked group isreached after which it continues to step over the outlets of the groupin search of a free outlet. When such an outlet is encountered relay HXoperates in a circuit from earth over contact p2, wiper Y2, one of thecontacts 6, 11, 16marked group contacts in the bank of wiper x4, relayHX, test wiper X3 to battery on the test bank contact. Contact haveopens, stopping further driving of the switch and contact hat]. shortcircuits the high resistance winding of relay HX to mark the outletengaged. The speaking wires are switched through at contacts 71x2 andM23 to wipers X6 and X7 and relay A is released and battery isdisconnected from wire a, signalling to the register controller thatimpulsing may be resumed. Relays P and R remain operated.

If all the outlets of the group connected to switch X are busy theswitch is brought to rest on contacts next after those connected to thelast outlet of the group by the operation of relay X to a batteryconnection to contacts 6, ll, 16 in the bank of wiper X3. Thecorresponding contacts in the banks of wipers X6 and X? are notconnected and the circuits over wires a and b are opened, therebyeffecting release of the register controller and switches subsequent tothe first selector which remains held over the calling loop and fromwhich a busy signal is given.

The release ofthe preceding switches, whether due to the above or torelease of the first selector by the calling subscriber clearingdisconnects earth from wire 0 and releases relay B. Contact b3 fallingback closes a homing circuit over wiper X1 for switch X and the switchis returned to its normal position. Switch Y performs only a huntingfunction, and, therefore, need not be returned to a normal position, butit may be so restored if required by connecting magnet YDM over itsself-interrupting contact and a back contact 01' 192 to a homing wiperY1 and earthed segment as shown in the drawings. If, however, switch Yhas no normal position, winding (I) of relay C will be connected directto wiper X5 and no advantage is gained by transposing the connectionbetween the banks of wipers Y2 and X4.

Fig. 2 shows an arrangement suitable for use in a direct impulsingsystem, and, for the sake of example, a pair of single-motion switcheshaving banks of twenty-five contacts each are used as a selector. Eachswitch has eight wipers and corresponding contact banks and outlets to afurther switching stage or other circuits are grouped, a group ofoutlets being connected to the banks of one switch, part of the groupbeing in one bank and part in another, simultaneous search over theoutlets in the two banks being provided for. As regards the groupsthemselves alternate groups are connected; different switches, thus, theodd groups are connected to switch Xandthe even groups to switch Y,diii'erentiation between the groups being pro- 'vided by a pair ofrelays P and Q. successive impulsesof a train being repeated toalternate switches.

The selector tests free by reason of battery potential on the test Wireand: whenseizedconnects earth to. the test, wire to mark it engaged andto hold preceding selectors during the setting operation, the holdingearth being returned from a succeeding switch on its seizure When theselector is picked up relay C operates by means of its winding. (I) overthe test wire in series with the test relay of the preceding selectorwhich switches through and operates relay A. Contact cl prepares theimpulsing circuit for the switch, magnets, contact 02 opens a homingcircuit for the switches and contacts c3 and 04 open the; circuits ofthe test relays HA and HB during-group selection. Relay A operating,contact a1 closes the circuit of relay B, which opcrates, and at contactb1 connects earth to the incoming test wire to hold preceding switchesand to mark the selector engaged. Contact b2 opens apointin the homingcircuit of switch X, contact b3 further prepares the impulsing circuitfor the switch magnets, contact b4 prepares the circuit of relay P, andcontact b5 that of relay Q, contacts b6 and b7. close points in thecircuits of the test relays. Impulses for the setting of the selectorare now transmitted to relay A which responds. The first impulse isrepeated at contact al to relay P which operates by means of its.winding (I) and locks up over its contact 122 independently of relay Q.Contact all) p1 connects winding (1) of relay Q to the impulse repeatingcircuit but the Winding is short tact ydm, magnet YDM to battery; aparallel circuit is closed for magnet XDM, the magnets XDM and YDMoperate, and step the wipers of both switches to the second bankcontacts. The

, off-normal contacts :cnl, $122, 11111, and 11112 are operated,contacts rnl and ynl opening the circuit of winding (I) of relay C toleave that relay dependent for continued energization on impulsing. Atthe. end of the impulse, relay A releases and the short circuit isremoved from winding (I) of relayQ. Relay Q operates over this windingin series with winding (I) of relay P and at contact ql opens a point inthe energizing circuit of relay P. Contact q3 opens a further point inthis circuit and in conjunction with contact a2 prepares a circuit ,forwinding (II) of relay Q. Thus, atthe end of the first impulse, relays Pand Q are operated and switch X is connected up with itswipers restingonits second contacts which are the contacts associated with thefirstoutlet of the first group; switch Y is resting with its wipers onits second contacts which are associated with the first outlet of thesecond group, but the. wipers are not connected. In the example taken itwill be assumed that the outlets of the first group are connected tocontacts 2 6, those of the third group to contacts 8-12, those of thefifth group to contacts 1418, and those of the seventh group to contacts20 -23, all in the banks of switch X. The outlets of the even groups areconnected to similarly numbered contacts in the bank of switch Y; I I Ileases due to the commencement of a second impulse a circuit is closedfrom earth over contact b3, winding (II) of relay C, contacts 01, p3,

wiper Y2 and second. bank contacts, commoned contacts 2-7 in the bank ofwiper X1, contacts xdm, magnet XDM to battery. The magnet operates andby means of its contact acdm, steps the wipers of switch X to contacts8. Switch Y is now connected up with its wipers resting on contacts 2which are associated with the first outlet of thesecond group and switchX is resting with its contacts resting on contacts 8 associated with thefirst outlet of the third group but its speaking and test wire wipersare disconnected at contacts p4, p5, p6, p7, g5, and qfi, which contactsconnect the speaking and test wires wipers Y3--Y8. I

If a third impulse is transmitted relay P is operated and a circuit isclosed over the front of contacts 113, wiper X2 and its eighth bankcontact, commoned contact 2-47 in the bank of wiper Y1 for magnet YDM.The switch Y is stepped to, its eighth contacts and its wipers Y2'Y8 aredisconnected at contacts of relays P and Q which connect in circuitwipers X2--X3 which are now resting on the first outlets of the 7 thirdgroup. Further impulses effect the alternate stepping of switches X andY in a similar manner.

At the end of the impulse train relay (3 releases and search over theoutlets of the required group takes place. For the sake of example itwill be assumed that an odd number of im-- pulses have been received andin consequence relays P and Q are operated and locked up over theirwindings (I) connecting switch X in circuit. On the release of relay Cthe test relays HA and HB are connected to earth over contact bland theimpulsing circuit for the switch magnets is opened at contact cl. Astepping circuit is closed, however, at contact 02 for the magnet oftheswitch which is to search, in the example switch X. Magnet XDM,therefore, energizes in a circuit over contacts :cdm, 3on2, g4, 02,hafi, 11b5, toearth and the wipers are stepped over con tacts connectedto outlets of an odd group,

test for a free outlet being made simultaneously by relays HA and HB.Wipers X3, X4, and X5 give access to one set of outlets of a group andwipers X6, X7, and X8 to another set, and when a free outlet in one ofthe sets is encountered, the

corresponding test relay operates. Assuming for a moment that a freeoutlet is encountered in the first-mentioned set, relay HA operates in acircuit from earth over contacts 121, ha2, b6, 03, winding (I) of relayHA, contact 106, wiper X5,

and bank contact'to battery connected to the extend the speaking wiresand disconnect relay A, and contact ha5 opens the magnet circuit toprevent further stepping, contact ha6 opens to prevent release of relayQ when relay A releases and contact ha? closes a holding circuit forrelays P and Q against the release of relay B which takes place shortlyafter the release of relay A. If the first free outlet is found in thebank of wipers X6-.-X8, relay HB operates and similar operations ensue.If, however, a free outlet is found simultaneously in both sets bothtest relays operate but relay HA on operation closes a hold ing circuitfor itself at contact hal and opens the locking circuit of relay HB sothatthe latter is not held but is released by the subsequent opening ofcontact 127.

Should all the outlets in the group be engage the wipers are brought torest on busy contacts immediately succeeding those connected to outlets.These contacts are numbered 7, 13, 19, and 2%. Relay HA operates overthese contacts and relay S, which is connected to them in the test banksand relay HA, locks up. Relay A is held in a circuit from battery overits right-hand winding, busy contact in the bank of wiper X4, contacts:05, hal, the calling loop, contacts .7013, p4, wiper X3, and busycontacts, left-hand winding of the relay, front contact 81, contactscontrolled by a busy signal cam device to earth and the subscriberreceives a busy signal.

Precisely similar operations take place if switch Y is used instead ofswitch X.

As only twenty-five contacts are provided in the banks of each switchthe number of groups would usually not exceed eight, except in caseswhere some of the groups are very small. It will be assumed then thateight groups only are provided. At the commencement of the eighthimpulse relay P is released, switch X is stepped from its twentiethcontact to the twenty-fifth, while switch Y remains on contacts 20. If aninth impulse is dialled relay P is reoperated and a circuit is closedover the twenty-fifth bank contact and wiper twentieth bank contact andwiper Y1 for magnet YDM and switch Y is stepped to its twenty-fifthcontact. The test relay HA operates immediately over a batteryconnection shown and a circuit is closed over the secondary of thetransformer N U T and twenty-fiith contact in the banks of wiper X3 tothe a wire and the subscriber receives a distinctive tone informing himthat he has dialled a non-existent number.

Similarly, if is dialled, relay P will release at the commencement ofthe last impulse but there will be no circuit for magnet XDM and thesubscriber will receive the tone as described above.

The selector is released by disconnection of earth from the test wire ina succeeding'circuit. The test relay releases and opens the speaking andtest wire circuits, releases relays P and Q if 0 erated, and preparesthe operating circuit of relay P. A homing circuit for the switchmagnets is closed as followsz-earth over contacts hb5, ha; 02, then overcontacts 122, amZ, to magnet XDM and over contacts q l yn2 to YDM andswitch.

2. A switching device comprising two automatic switches, groups ofoutlets accessible to each switch, means for causing either switch tohunt for and connect with an idle outlet in a marked group of outlets,and means in each of said switches for marking outlet groups in theother of said switches.

3. A switching device comprising two singlemotion switches, groups ofoutlets accessible to said switches, means for operating either switchto designate a particular group of outlets accessible to the otherswitch, and means for operating the said other switch to hunt for andconnect with an idle outlet in the designated group.

4. In a telephone system, a trunk line, a switching device comprisingtwo automatic switches terminating said trunk lines, groups of outletsaccessible to said svitches, means for operating either switch todesignate a particular group of outlets accessible to the other switch,and means for causing said other switch to connect said trunk line withan idle outlet in the designated group.

5. In a telephone system, two selective switches, groups of outletsaccessible to said switches, means in each switch for marking groups ofoutlet groups accessible to the other switch, and means in each switchfor selecting an idle outlet in a group marked by the other switch.

6. In a telephone system, two selective switches, groups of outletsdivided into sub-groups accessible to the respective switches, means forseizing said switches simultaneously, means for causing the first switchto hunt for an idle outlet in one of said sub-groups, and automaticmeans for causing the other switch to hunt for an idle outlet in thecorresponding sub-group when all outlets in said one sub-group are busy.

7. In a telephone system, a selector comprising two single-motionswitches, a group of outlets part of which are accessible to one of saidswitches and the remaining of which are accessible to the other of saidswitches, means for operating said one switch to hunt over theaccessible outlets of the group for an idle outlet, and means responsiveto the failure of said one switch to find an idle outlet for operatingthe other of said switches to hunt over the remaining outlets of thegroup for an idle outlet.

8. In a telephone system, two selective switches, groups of outletsaccessible to said switches, means for directively operating the firstswitch to mark a group of outlets accessible to the second switch, meansfor causing the second switch to hunt for an idle outlet in the markedgroup, means in the second switch for marking a corresponding group ofoutlets accessible to said first switch when all outlets of the firstmarked group are engaged, and means for causing said first switch tohunt for an idle outlet in the second marked group.

9. A switching device comprising two automatic switches, groups ofoutlets divided into subgroups accessible to respective ones of saidswitches, means including one switch for marking a sub-group of outletsto cause the other switch to hunt for an idle outlet therein, and meansincluding the other switch effective in case no idle outlets areavailable in the marked sub-group for marking the correspondingsub-group accessible to said one switch to cause the same to hunt for anidle outlet therein.

10. In'combination, a switching device comprising two single-motionswitches, groups of outlets divided into sub-groups accessible to therespecto hunt for anidle outlet in the marked subgroup, means forcausing said other switch to mark the corresponding sub-group accessibleto said one switch responsive to all trunks of the first sub-group beingfound busy, and means for an idle outlet 11. In a telephone system, wesingle-inotion switches, wipers for said switches, groups of con tactsets accessible to the respective switches via their wipers, means fordirectively operating the first switch to position its wipers on a setoicontacts to marl: a particular group of contact sets accessible to thesecond switch, means for moving the wipers of the second switch over themarked contact group in search of an idle contact set and to a positionbeyond the last contact set in the group in case no idle contact setsare ava11-=' able, and means including a wiper of said second switchthereafter effective to mark a particular group of contact setsaccessible to said first switch. i

12. In a telephone system, two automatic switches, each of which isadapted to mark groups of outlets accessible to the other switch andeach of which is adapted to'hunt for. an idle outlet in a marked group,means for directively operating one switch to initiate the marking andhunting operations, and means for restoring both switches to normalposition.

13. In ,a telephone system, a trunk line, two. automatic switches eachof which is adapted to mark groups of outlets accessible tothe otherswitch and eachof' which is adapted to hunt for an idle outlet in amarked group, and meansczontrolled over the trunk line fordirectivelyoperating one switch to initiate the marking and hunting operationswhereby said line is connected with an idle outlet accessible to one orthe other of said switches.

14. In a telephone system, a switching device comprising two automaticswitches each of which is adapted to control the hunting operation ofthe other by designating a particular group of outlets to be huntedover, and groups of outlets divided into sub-groups accessible totherespec ,,tive switches so arranged that the order of access tocorresponding subgroups is'reversed for the switches. a

:15. A switching device comprising two automatic switches, means in thedevice responsive .to a series of impulses, and means including saidlast means for operating said switches simultaneously responsive to thefirst impulse of the series and for operating said switches alternatelyresponsive to succeeding impulses of the series.

16. A switching device comprising two automatic switches, groupsof-outlets accessible to said switches, means for alternately causingeach switch to mark a particular group of outlets accessibleto the otherswitch, and means for causing the said other switch. to pass over themarked outlet group. i H

17. A switchingdevice comprising two automatic switches, two sets ofwipers for each switch, groups of outlets accessible to the respectiveswitches via said wipers, means in the device for determining theparticular switch to be used in a connection, and means in'the devicefor determiningthe particular set of wipers of said particular switchwhich are to connect withone of said outlets. V

18. In a telephone system, a switching device comprising twostep-by-step switches, means for 19. In a telephone system, a trunk linetermimating in a switching device comprising two autoc s t itcheswipersfor the switches, means itting a series of impulses over the deviceenergized and dcon ve to alternate impulses-of the series, and rns'controlled by said relays for connecting thetrunlrlineto' the wipersof either of said switches.

as. In a telephone system,a trunk line terminating in a switching devicecomprising two automatic switches, groups of outlets accessible to theswitches, means fortransm-itting digit impulses over the trunk line,means inthe device for responding to said digit impulses, means forcausing eitherof the switches to hunt for an idle outlet in anaccessible group responsive to the receipt of a digit designating thatparticular operate said switches alternately, a

group, and means for applying a distinctive tone to the trunk lineresponsive to the receipt of a digit greater than the number of outletgroups accessible to said switches. 1

21. In an automatic switch, means for receiving a series of impulses,means for operating the switch one step responsive to the first oddnumbered impulse of the series, and means for operating the switch aplurality of steps responsive to each subsequent even numbered impulseof the V series.

22. In an automatic'switchhaving access to groups of contacts, a controlrelay, means for operating and releasing said relay, means responsive tothe operation of said relay for advancing the switch one step to thefirst contact of one of said groups, and means responsive to the releaseof said relay for advancing the switch a plurality of steps to the firstcontact of a succeeding group.

23. Inan automatic switch, means for receiving a series of impulses,means for operating the switch one step responsive to the first odd numbered impulse of the series/and means for opcrating the switch aplurality of steps responsive to each subsequent odd numbered impulse ofthe tic.

sponsive to the receipt of a series of impulses for setting each switchin selective relation with a group of outlets, and means dependent onthe V 7 value of the impulse series for determining which one of theswitches is to huntfor an idle outlet in a selected group.

26. In combination, a switching device comprising two separate switches,groups of outlets accessible to the respective switches, means fortransmitting a series of impulses to said device to set each of saidswitches in selective relation with a group of trunks accessiblethereto, means operative in case the impulse series consists of an evennumber of impulses for causing one switch to hunt for an idle outlet inits selected group, and means operative in case the impulse seriesconsists of an oddlnumber of impulses for causing the other switch tohunt for an idle outlet in its selected group.

2'7. In combination, a switching device com prising two separateswitches, groups of outlets accessible to the respective switches, acontrol relay, means for energizing and deenergizing said relayresponsive respectively to alternate impulses of a received impulseseries, means controlled by said relay for operating-said switchesalternately to set them in selective relation with groups of outlets,and means controlled by said relay for determining which of saidswitches is to hunt for an idle outlet in a selected group.

28. In a switching device, four separate sets of wipers, groups ofcontacts accessible to said wipers, means responsive to the receipt of aseries of impulses for setting said wipers in selective relationwithgroups of outlets, means controlled by the value of the impulse seriesfor selecting a pair of said wiper sets, and means for automaticallyselecting a particular wiper set of the selected pair.

29. A switching device as claimed in claim 27 in which the selection ofa particular Wiper set of a selected pair is controlled by the busy oridle condition of outlets accessible to the wiper sets.

30. In combination, a switching device comprising two switches, acontrol relay in said device, means for repeatedly energizing anddeenergizing said relay responsive to a series of impulses received bythedevice, means responsive to the initial energization of the relay foroperating both switches one step, means responsive to each subsequentenergization of the relay for operating one switch a plurality of steps,and means responsive to each deenergization of the relay for operatingthe other switch a plurality of steps.

ALEXANDER JOHN ESCOTT;

